1. Field of the Invention
The present invention relates to a zero pressure accumulator conveyor and, more particularly, to an accumulator conveyor in which delivery or non-delivery of the propelling force to the article is pneumatically controlled and applied to a plurality of article supporting rollers simultaneously.
2. Description of the Prior Art
The use of expansible tube means in combination with a pressurized pneumatic system has been known in the prior art for controlling the propulsion of articles along a conveyor system. This type of system is disclosed in U.S. Pat. No. 3,770,102 issued to DeGood on Nov. 6, 1973. The patent to DeGood discloses an accumulator conveyor having a powered propelling member passing through a plurality of independent operating zones arranged in tandem along the conveyor. In each zone the propelling member is shiftable between an article propelling and an article non-propelling position by pneumatically actuated pressure rollers acting on a propelling member. A valve operated by an article detecting sensor in each zone, operates a supply or exhaust fluid pressure to the actuators. An auxiliary valve system connected between the secondary pressure source and the actuators operates to shift all of the operating zones into an article propelling position, thereby overriding the accumulative function of the conveyor.
In U.S. Pat. No. 3,724,642 issued to DeGood on Apr. 3, 1973, there is disclosed a powered roller accumulator similar to the one discussed above. However, the patent also discloses a brake means which engages the powered rollers in order to stop the rotation when the propelling member is shifted to a non-driving position, thereby preventing movement of articles along the conveyor.
However, both of the disclosed systems apply a braking apparatus to a singular roller in each tandem section of the conveyor. If additional rollers are to be afforded braking pressure, the mechanism must be duplicated at various positions in each section. Thus, the braking device as disclosed is unable to be applied to a plurality of article carrying rollers simultaneously. An article moving on the conveyor will not be stopped until it reaches the braking roller, and thus, an article traveling behind the first article will come into contact therewith, and apply pressure thereto in order to be stopped. It can be readily seen that the braking roller would be required to be spaced a distance apart that is less than the dimension of the article being propelled along the conveyor, in order to reduce the amount of pressure between articles that are stopped. The cost and inconvenience of providing a large quantity of braking rollers is readily overcome with the use of the instant invention.
In U.S. Pat. No. 3,323,636 issued to Gotham on June 6, 1967, there is disclosed a power driven roller conveyor which is driven from below by a moving belt urged into contact with the rollers by spring-actuated pulleys which limit the frictional driving force on the several driven rollers. The rollers require continual adjustment in order to insure the proper amount of frictional contact between the moving belt and the rollers, since the spring tension varies with time and teperature. A braking means for stopping the moving articles on the conveyor is not disclosed therein.